Summary/ abstract: Poor retention in HIV primary care results in lower rates of HIV viral suppression, higher rates of HIV transmission, and exacerbates racial and ethnic disparities in health outcomes, including survival. To date, there are no interventions that effectively relink and retain PWH in care when they are found outside the HIV clinic. Many persons with HIV infection (PWH) are hospitalized with life-threatening but preventable complications of inadequately treated HIV infection. They are among the most important patients to retain in care. Our previous research shows that among PWH who are out of care and hospitalized, avoidance coping, stigma, and mental health difficulties were nearly universal. Further, avoidance coping was a predictor of failure to re-engage in care after discharge. Acceptance and Commitment Therapy (ACT) is a transdiagnostic intervention with the capacity to address a range of psychosocial and behavior-related issues that PWH experience. ACT helps patients overcome avoidance, particularly avoidance of uncomfortable internal states and the situations that trigger such states, by promoting acceptance-based coping and re-engagement in meaningful and valued-life activities. Brief ACT interventions appear to be feasible, acceptable, and at least preliminarily, have efficacy. We propose to develop, refine, and pilot a brief (4-5 contact hours) ACT intervention for hospitalized, out-of-care PWH. `Targeting HIV Retention and Improved Viral load through Engagement' (`THRIVE') will aim to help patients overcome avoidance, a maladaptive coping strategy implicated in a range of problems, including depression, anxiety, substance abuse, and HIV-related self-stigma, all of which constitute barriers to care. Delivering THRIVE in the hospital with a phone booster session after discharge will increase therapy initiation and completion, the lack of which is often the greatest obstacle to effective delivery of mental health services for PWH. In Aim 1, a brief hospital-based transdiagnostic, individually delivered ACT intervention (THRIVE) tailored specifically for out-of-care hospitalized PWH will be developed. Input from a multi-disciplinary team of expert care providers and PHW will be utilized to create the therapist protocol and patient workbook. We will then pilot THRIVE in 10 hospitalized out-of-care PWH who will provide qualitative feedback on the intervention. The feedback, along with input from patients and the multi-disciplinary team, will be used to refine THRIVE. In Aim 2, we will conduct a pilot randomized clinical trial (RCT) of the refined THRIVE intervention (N=35) compared to treatment as usual (N=35). This pilot RCT will 1) evaluate feasibility and acceptability for a full- scale RCT; and 2) examine trends in outcomes of interest for the definitive RCT. We will then be positioned to submit a separate grant to test the efficacy of THRIVE in a fully powered randomized trial. This work has the potential to decrease HIV morbidity and racial/ethnic disparities and contribute to ending the HIV epidemic in the United States, which are NIH priorities.